Method and apparatus for controlling transmit power in wireless communication system

ABSTRACT

A method and apparatus of controlling transmit power in a wireless communication system is provided. A wireless apparatus selects one transmit mode among a plurality of transmit modes, and determines the transmit power on the basis of the selected transmit mode. The wireless apparatus transmits an uplink channel by using the transmit power.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is the National Phase of PCT/KR2010/006096 filed onSep. 8, 2010, which claims priority under 35 U.S.C. 119(e) to U.S.Provisional Application No. 61/240,652 filed on Sep. 8, 2009 and under35 U.S.C. 119(a) to Patent Application No. 10-2010-0087344 filed inRepublic of Korea on Sep. 7, 2010, all of which are hereby expresslyincorporated by reference into the present application.

TECHNICAL FIELD

The present invention relates to wireless communication, and moreparticularly, to a method and apparatus for controlling transmit powerin a wireless communication system.

BACKGROUND ART

Long term evolution (LTE) based on 3rd generation partnership project(3GPP) technical specification (TS) release 8 is a promisingnext-generation mobile communication standard.

As disclosed in 3GPP TS 36.211 V8.5.0 (2008-12) “Evolved UniversalTerrestrial Radio Access (E-UTRA); Physical Channels and Modulation(Release 8)”, a physical channel of the LTE can be classified into adata channel, i.e., a physical downlink shared channel (PDSCH) and aphysical uplink shared channel (PUSCH), and a control channel, i.e., aphysical downlink control channel (PDCCH), a physical control formatindicator channel (PCFICH), a physical hybrid-ARQ indicator channel(PHICH), and a physical uplink control channel (PUCCH).

A PDCCH (i.e., a downlink control channel) carries a downlink grant forreceiving the PDSCH of a UE (UE) and an uplink grant for transmittingthe PUSCH of a UE. A PUCCH (i.e., an uplink control channel) carries anuplink control signal (e.g., ACK (positive-acknowledgement)/NACK(negative-acknowledgement) signals for a HARQ), a CQI (Channel QualityIndicator) indicating the condition of a downlink channel, an SR(Scheduling Request) for requesting the allocation of radio resourcesfor uplink transmission, and so on.

To guarantee a higher data rate, a technique using a multi-antenna hasbeen introduced.

Through transmit diversity and spatial multiplexing, multiple antennatransmission can achieve higher link performance compared to singleantenna transmission.

The conventional 3GP LTE does not support multiple antenna transmissionin uplink. However, as a next generation communication system employsthe multiple antenna uplink, uplink transmit power is needed to considermultiple antenna transmission.

DISCLOSURE OF INVENTION Technical Problem

The present invention provides a method and apparatus for performing anHARQ using a plurality of resources and a plurality of antennas.

Solution to Problem

In an aspect, a method of controlling a transmit power in a wirelesscommunication system is provided. The method includes selecting onetransmit mode among a plurality of transmit modes, determining thetransmit power on the basis of the selected transmit mode, andtransmitting an uplink channel by using the transmit power.

The plurality of transmit modes may include a multiple-antenna transmitmode and a single-antenna transmit mode.

The plurality of transmit modes may be determined based on the number oftransmit antennas.

The uplink channel may be a physical uplink shared channel (PUSCH) or aphysical uplink control channel (PUCCH).

The step of determining of the transmit power on the basis of theselected transmit mode may include adding a transmit power control valuecorresponding to the selected transmit mode to transmit power for theuplink channel.

One of transmit mode may be selected among the plurality of transmitmodes on the basis of a resource allocated to the uplink channel.

If the number of resources allocated to the uplink channel is greaterthan 1, a multiple-antenna transmission mode may be selected, and if thenumber of resources allocated to the uplink channel is 1, asingle-antenna transmission mode may be selected.

A resource allocated to the uplink channel may be obtained based on aresource used to transmit a downlink control channel.

In another aspect, a wireless apparatus includes a plurality ofantennas, a transceiver configured for transmitting an uplink channelthrough the plurality of antennas by using transmit power, and atransmit power controller configured for selecting one transmit modeamong a plurality of transmit modes and determining the transmit poweron the basis of the selected transmit mode.

Advantageous Effects of Invention

As a user equipment switches a transmit mode, a transmit power can beadjusted. Therefore, link performance can be improved.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram showing a wireless communication system.

FIG. 2 is a diagram showing the structure of a radio frame in the 3GPPLTE.

FIG. 3 is a diagram showing the structure of a downlink subframe in the3GPP LTE.

FIG. 4 is a diagram showing an example of the resource mapping ofPDCCHs.

FIG. 5 is an exemplary view showing the monitoring of PDCCHs.

FIG. 6 is a diagram showing an example of an uplink subframe in the 3GPPLTE.

FIG. 7 is a diagram showing a PUCCH format 1 in a normal CP in the 3GPPLTE.

FIG. 8 is a diagram showing a PUCCH format 1 in an extended CP in the3GPP LTE.

FIG. 9 is a diagram showing an example in which an HARQ is performed.

FIG. 10 is a diagram showing an example in which an ACK/NACK signal istransmitted in a multi-antenna.

FIG. 11 is a diagram showing a method of determining a plurality ofresources.

FIG. 12 is a flowchart showing a transmission power control methodaccording to an embodiment of the present invention.

FIG. 13 is a block diagram showing a wireless apparatus for implementingan embodiment of the present invention.

MODE FOR THE INVENTION

FIG. 1 is a diagram showing a wireless communication system. A wirelesscommunication system 10 includes one or more base stations (BSs) 11.Each of the BSs 11 provides communication services to a specificgeographical area (in general referred to as a cell) 15 a, 15 b, or 15c. Each of the cells can be divided into a plurality of regions(referred to as sectors).

A user equipment (UE) 12 may be fixed or mobile, and may be referred toas another terminology, such as a mobile station (MS), a mobile terminal(MT), a user terminal (UT), a subscriber station (SS), a wirelessdevice, a personal digital assistant (PDA), a wireless modem, a handhelddevice, etc.

The BS 11 is generally a fixed station that communicates with the UE 12and may be referred to as another terminology, such as an evolved node-B(eNB), a base transceiver system (BTS), an access point, etc.

Hereinafter, downlink implies communication from the BS to the UE, anduplink implies communication from the UE to the BS. In the downlink, atransmitter may be a part of the BS, and a receiver may be a part of theMS. In the uplink, the transmitter may be a part of the UE, and thereceiver may be a part of the BS.

FIG. 2 is a diagram showing the structure of a radio frame in the 3GPPLTE. The section 6 of 3GPP TS 36.211 V8.5.0 (2008-12) “Evolved UniversalTerrestrial Radio Access (E-UTRA); Physical Channels and Modulation(Release 8)” may be incorporated herein by reference. A radio frameconsists of 10 subframes indexed with 0 to 9. One subframe consists of 2slots. A time required for transmitting one subframe is defined as atransmission time interval (TTI). For example, one subframe may have alength of 1 millisecond (ms), and one slot may have a length of 0.5 ms.

One slot may include a plurality of orthogonal frequency divisionmultiplexing (OFDM) symbols in a time domain. Since the 3GPP LTE usesorthogonal frequency division multiple access (OFDMA) in a downlink, theOFDM symbol is only for expressing one symbol period in the time domain,and there is no limitation in a multiple access scheme or terminologies.For example, the OFDM symbol may also be referred to as anotherterminology such as a single carrier frequency division multiple access(SC-FDMA) symbol, a symbol period, etc.

Although it is described that one slot includes 7 OFDM symbols forexample, the number of OFDM symbols included in one slot may varydepending on a length of a cyclic prefix (CP). According to 3GPP TS36.211 V8.5.0 (2008-12), in case of a normal CP, one subframe includes 7OFDM symbols, and in case of an extended CP, one subframe includes 6OFDM symbols.

A resource block (RB) is a resource allocation unit, and includes aplurality of subcarriers in one slot. For example, if one slot includes7 OFDM symbols in a time domain and an RB includes 12 subcarriers in afrequency domain, one RB can include 7×12 resource elements (REs).

A primary synchronization signal (PSS) is transmitted in last OFDMsymbols of a 1st slot, i.e., a 1st slot of a 1st subframe (a subframeindexed with 0), and an 11th slot, i.e., a 1st slot of a 6th subframe (asubframe indexed with 5). The PSS is used to obtain OFDM symbolsynchronization or slot synchronization, and is in association with aphysical cell identify (ID). A primary synchronization code (PSC) is asequence used for the PSS. There are three PSCs in the 3GPP LTE. One ofthe three PSCs is transmitted using the PSS according to a cell ID. Thesame PSC is used for each of the last OFDM symbols of the 1st slot andthe 11th slot.

A secondary synchronization signal (SSS) includes a 1st SSS and a 2ndSSS. The 1st SSS and the 2nd SSS are transmitted in an OFDM symboladjacent to an OFDM symbol in which the PSS is transmitted. The SSS isused to obtain frame synchronization. The SSS is used to obtain a cellID together with the PSS. The 1st SSS and the 2nd SSS use differentsecondary synchronization codes (SSCs). If the 1st SSS and the 2nd SSSeach include 31 subcarriers, sequences of two SSCs with a length of 31are respectively used for the 1st SSS and the 2nd SSS.

A physical broadcast channel (PBCH) is transmitted in four precedingOFDM symbols of a 2nd slot of the 1st subframe. The PBCH carriesnecessary system information required by a UE to communicate with a BS.System information transmitted through the PBCH is referred to as amaster information block (MIB). In comparison thereto, systeminformation transmitted through a physical downlink control channel(PDCCH) is referred to as a system information block (SIB).

As disclosed in 3GPP TS 36.211 V8.5.0 (2008-12), the LTE classifies aphysical channel into a data channel, i.e., a physical downlink sharedchannel (PDSCH) and a physical uplink shared channel (PUSCH), and acontrol channel, i.e., a physical downlink control channel (PDCCH) and aphysical uplink control channel (PUCCH). Further, there is a downlinkcontrol channel, i.e., a physical control format indicator channel(PCFICH) and a physical hybrid-ARQ indicator channel (PHICH).

FIG. 3 is a diagram showing the structure of a downlink subframe in the3GPP LTE. A subframe is divided into a control region and a data regionin a time domain. The control region includes up to three preceding OFDMsymbols of a 1st slot in the subframe. The number of OFDM symbolsincluded in the control region may vary. A PDCCH is allocated to thecontrol region, and a PDSCH is allocated to the data region.

Control information transmitted through the PDCCH is referred to asdownlink control information (DCI). The DCI may include resourceallocation of the PDSCH (this is referred to as a downlink grant),resource allocation of a PUSCH this is referred to as an uplink grant),a set of transmit power control commands for individual UEs in any UEgroup and/or activation of a voice over Internet protocol (VoIP).

A PCFICH transmitted in a 1st OFDM symbol in the subframe carriesinformation regarding the number of OFDM symbols (i.e., a size of thecontrol region) used for transmission of control channels in thesubframe.

A PHICH carries an acknowledgement (ACK)/not-acknowledgement (NACK)signal for uplink hybrid automatic repeat request (HARM). That is, theACK/NACK signal for uplink data transmitted by the UE is transmittedover the PHICH.

FIG. 4 is a diagram showing an example of the resource mapping ofPDCCHs. The section 6 of 3GPP TS 36.211 V8.5.0 (2008-12) may beincorporated herein by reference. R0 denotes a reference signal of a 1stantenna, R1 denotes a reference signal of a 2nd antenna, R2 denotes areference signal of a 3rd antenna, and R3 denotes a reference signal ofa 4th antenna.

A control region in a subframe includes a plurality of control channelelements (CCEs). The CCE is a logical allocation unit used to providethe PDCCH with a coding rate depending on a radio channel state, andcorresponds to a plurality of resource element groups (REGs). Accordingto an association relation of the number of CCEs and the coding rateprovided by the CCEs, a PDCCH format and a possible number of bits ofthe PDCCH are determined.

One REG (indicated by a quadruple in FIG. 4) includes 4 REs. One CCEincludes 9 REGs. The number of CCEs used to configure one PDCCH may beselected from a set {1, 2, 4, 8}. Each element of the set {1, 2, 4, 8}is referred to as a CCE aggregation level.

A control channel consisting of one or more CCEs performs interleavingin an REG unit, and is mapped to a physical resource after performingcyclic shift based on a cell identifier (ID).

FIG. 5 is an exemplary view showing the monitoring of PDCCHs. For themonitoring of PDCCHs, reference can be made to section 9 of 3GPP TS36.213 V8.5.0 (2008-12). In the 3GPP LTE, blind decoding is used todetect PDCCHs. Blind decoding is a method of demasking a specific ID forthe CRC of a received PDCCH (referred to a candidate PDCCH) and checkingCRC error in order to determine whether the corresponding PDCCH is itsown control channel. A UE does not know that its own PDCCH istransmitted using which CCE aggregation level or which DCI format atwhich position within the control region.

A plurality of PDCCHs can be transmitted in one subframe. A UE monitorsthe plurality of PDCCHs every subframe. Monitoring is an operation ofattempting PDCCH decoding by the UE according to a format of themonitored PDCCH.

The 3GPP LTE uses a search space to reduce an overload caused by blinddecoding. The search space can be called a monitoring set of CCEs forPDCCHs. A UE monitors the PDCCHs within a corresponding search space.

The search space is classified into a common search space and aUE-specific search space. The common search space is a space forsearching for a PDCCH having common control information and consists of16 CCEs indexed with 0 to 15. The common search space supports a PDCCHhaving a CCE aggregation level of {4, 8}. The UE-specific search spacesupports a PDCCH having a CCE aggregation level of {1, 2, 4, 8}.

A method of transmitting an ACK/NACK signal through the PUCCH in the3GPP LTE is described below.

FIG. 6 is a diagram showing an example of an uplink subframe in the 3GPPLTE. The uplink subframe can be divided into a control region to which aphysical uplink control channel (PUCCH) carrying uplink controlinformation is allocated and a data region to which a physical uplinkshared channel (PUSCH) carrying uplink data is allocated. A PUCCH for aUE is allocated in a pair of resource blocks in a subframe. Resourcesblocks belonging to the resource block-pair occupy different subcarriersin a first slot and a second slot. In FIG. 6, m is a position indexindicating a logical frequency region position of the resource blockpair, allocated to PUCCHs within the uplink subframe. FIG. 6 shows thatresource blocks having the same m value occupy different subcarriers inthe two slots.

In accordance with 3GPP TS 36.211 V8.5.0 (2008-12), a PUCCH supports amultiple formats. PUCCHs having different numbers of bits per subframecan be used in accordance with a modulation scheme dependent on a PUCCHformat.

The table 1 shows an example of modulation schemes and the number ofbits per subframe according to PUCCH formats.

TABLE 1 PUCCH Format Modulation Scheme Number of Bits per subframe 1 N/AN/A 1a BPSK 1 1b QPSK 2 2 QPSK 20 2a QPSK + BPSK 21 2b QPSK + BPSK 22

The PUCCH format 1 is used to transmit an SR (Scheduling Request), thePUCCH formats 1 a/1 b are used to transmit an ACK/NACK signal for anHARQ, the PUCCH format 2 is used to transmit a CQI, and each of thePUCCH formats 2 a/2 b is used to simultaneously transmit a CQI and anACK/NACK signal. When only the ACK/NACK signal is transmitted in asubframe, the PUCCH formats 1 a/1 b are used, but when only the SR istransmitted in a subframe, the PUCCH format 1 is used. When the SR andthe ACK/NACK signal are simultaneously transmitted, the PUCCH format 1is used. The ACK/NACK signal modulated in resources to which the SR hasbeen allocated is transmitted.

Each of all the PUCCH formats uses the cyclic shift (CS) of a sequencein each OFDM symbol. The cyclic-shifted sequence is generated bycyclically shifting a base sequence by a specific CS amount. Thespecific CS amount is indicated by a CS index.

An example in which the base sequence r_(u)(n) is defined is shown as:

MathFigure 1r _(u)(n)=e ^(jb(n)π/4)  [Math. 1]

where u indicates a root index, n indicates an element index where0≦n≦N−1, and N indicates the length of the base sequence. b(n) isdefined in 3GPP TS 36.211 V8.5.0 (2008-12).

The length of the base sequence is equal to the number of elementsincluded in the base sequence. μ can be determined based on a cell ID(identifier) or a slot number within a radio frame. Assuming that thebase sequence is mapped to one resource block in the frequency domain,the length of the base sequence N is 12 because one resource blockincludes 12 subcarriers. A different base sequence can be defined on thebasis of a different root index.

A cyclic-shifted sequence r(n, I_(cs)) can be generated by cyclicallyshifting a base sequence r(n) as shown:

$\begin{matrix}{{MathFigure}\mspace{14mu} 2} & \; \\{{{r\left( {n,I_{CS}} \right)} = {{r(n)}E\;{\exp\left( \frac{{j2}\;\pi\; I_{CS}n}{N} \right)}}},{{0{DI}_{CS}{DN}} - 1}} & \left\lbrack {{Math}.\mspace{14mu} 2} \right\rbrack\end{matrix}$

where I_(cs) is a CS index indicating the CS amount (0≦Ics≦N−1).

Hereinafter, available CS indices of the base sequence refer to CSindices that can be derived from the base sequence on the basis of a CSinterval. For example, assuming that the length of the base sequence is12 and the CS interval is 1, a total number of available CS indices ofthe base sequence is 12. Assuming that the length of the base sequenceis 12 and the CS interval is 2, the number of available CS indices ofthe base sequence is 6.

A method of transmitting the HARQ ACK/NACK signal in the PUCCH formats1/1 a/1 b (hereinafter collectively referred to as a PUCCH format 1) isdescribed below.

FIG. 7 is a diagram showing the PUCCH format 1 in a normal CP in the3GPP LTE. FIG. 8 is a diagram showing the PUCCH format 1 in an extendedCP in the 3GPP LTE. The normal CP and the extended CP have differentpositions and different numbers of reference signals (RSs) because theyinclude different numbers of OFDM symbols in one slot, but have the sameACK/NACK transmission structure.

A modulation symbol d(0) is generated by modulating an 1-bit ACK/NACKsignal through BPSK (Binary Phase Shift Keying) or a 2-bit ACK/NACKsignal through QPSK (Quadrature Phase Shift Keying).

In the normal CP or the extended CP, one slot includes 5 OFDM symbolsfor transmitting the ACK/NACK signal. One subframe includes 10 OFDMsymbols for transmitting the ACK/NACK signal. The modulation symbol d(0)is spread with a cyclic-shifted sequence r(n, I_(cs)). Assuming1-dimensional spread sequence corresponding to an (i+1)th OFDM symbol ina subframe is m(i), {m(0), m(1), . . . , m(9)}={d(0)r(n, I_(cs)),d(0)r(n, IC_(cs)), . . . , d(0)r(n, I_(cs))}.

To increase UE capacity, the 1-dimensional spread sequence can be spreadusing an orthogonal sequence.

An orthogonal sequence w_(i)(k), where i is a sequence index and0≦k≦K−1, having a spreading factor K=4 may use the following sequence.

TABLE 2 Index (i) [w_(i)(0), w_(i)(1), w_(i)(2), w_(i)(3)] 0 [+1, +1,+1, +1] 1 [+1, −1, +1, −1] 2 [+1, −1, −1, +1]

The orthogonal sequence w_(i)(k), where i is a sequence index and0≦k≦K−1, having a spreading factor K=3 may use the following sequence.

TABLE 3 Index (i) [w_(i)(0), w_(i)(1), w_(i)(2)] 0 [+1, +1, +1] 1 [+1,e^(j2π/3), e^(j4π/3)] 2 [+1, e^(j4π/3), e^(j2π/3)]

A different spreading factor can be used for each slot. In the 3GPP LTE,the last OFDM symbol within a subframe is used in order to transmit anSRS (sounding reference signal). Here, in a PUCCH, a first slot uses thespreading factor K=4 and a second slot uses the spreading factor K=3.

Accordingly, assuming that a certain orthogonal sequence index i isgiven, 2-dimensional spread sequences s(0), s(1), . . . , s(9) can beexpressed as follows:

{s(0), s(1), . . . , s(9)}={w_(i)(0)m(0), w_(i)(1)m(1), w_(i)(2)m(2),w_(i)(3)m(3), w_(i)(4)m(4), w_(i)(0)m(5), w_(i)(1)m(7), w_(i)(2)m(8),w_(i)(3)m(9)}.

The CS index I_(cs) can vary depending on a slot number (ns) within aradio frame or a symbol index (l) within a slot or both. Assuming thatthe first CS index is 0 and the value of a CS index is increased by 1every OFDM symbol, {s(0), s(1), . . . , s(9)}={w_(i)(0)d(0)r(n, 0),w_(i)(1)d(1)r(n, 1), w_(i)(3)d(9)r(n,9)}, as shown in FIGS. 7 and 8.

The 2-dimensional spread sequences {s(0), s(1), . . . , s(9)} aresubject to IFFT and then transmitted through corresponding resourceblocks. Accordingly, the ACK/NACK signal is transmitted on the PUCCH.

The orthogonal sequence index i, the CS index L, and the resource blockindex m are parameters necessary to constitute a PUCCH and alsoresources used to distinguish PUCCHs (or UEs) from each other. Assumingthat the number of available CSs is 12 and the number of availableorthogonal sequence indices is 3, PUCCHs for a total of 36 UE can bemultiplexed to one resource block.

In the 3GPP LTE, in order for a UE to acquire the above three parametersfor constituting the PUCCH, a resource index n⁽¹⁾ _(PUCCH) is defined.The resource index n⁽¹⁾ _(PUCCH)=n_(CCE)+N⁽¹⁾ _(PUCCH). Here, n_(CCE) isthe number of first CCEs used to transmit a corresponding DCI (i.e., theallocation of downlink resources used to receive downlink datacorresponding to an ACK/NACK signal), and n⁽¹⁾ _(PUCCH) is a parameterthat a BS informs the UE through an upper layer message.

Consequently, it can be said that resources used to transmit a PUCCH areimplicitly determined depending on the resources of a correspondingPDCCH. This is because a UE does not separately inform a BS of resourcesused to transmit a PUCCH for an ACK/NACK signal, but indirectly informsthe BS of resources used for a PDCCH used to transmit downlink data.

FIG. 9 is a diagram showing an example in which an HARQ is performed. AUE monitors PDCCHs and receives a PDCCH 501, including a downlink grant,in an n-th subframe. The UE receives a downlink transport block througha PDSCH 502 indicated by the downlink grant.

The UE transmits an ACK/NACK signal for the downlink transport block onthe PUCCH 511 in an (n+4)th subframe. The ACK/NACK signal becomes an ACKsignal if the downlink transport block is successfully decoded and aNACK signal if the downlink transport block is unsuccessfully decoded.When the NACK signal is received, a BS can retransmit the downlinktransport block until the reception of an ACK signal or a maximum numberof retransmissions.

To constitute the PUCCH 511, the UE uses resource allocation of thePDCCH 501. That is, the lowest CCE index used to transmit the PDCCH 501becomes n_(CCE), and a resource index, such as n⁽¹⁾_(PUCCH)=n_(CCE)+N⁽¹⁾ _(PUCCH), is determined.

Hereinafter, referring to section 5 of 3GPP TS 36.213 V8.5.0 (2008-12),uplink transmit power in the 3GPP LTEE is disclosed.

The setting of the UE Transmit power P_(PUSCH) for the PUSCHtransmission in subframe i is defined by:

MathFigure 3P _(PUSCH)=min{P _(CMAX),10 log₁₀(M _(PUSCH)(i)))+P _(O) _(—)_(PUSCH)(j))+α(j)PL+Δ _(TF)(i)+f(i)}  [Math. 3]

where P_(CMAX) is the configured UE transmitted power, and M_(PUSCH)(i)is the bandwidth of the PUSCH resource assignment expressed in number ofresource blocks valid for subframe i. P_(O) _(—) _(PUSCH)(j) is aparameter composed of the sum of a cell specific nominal component P_(O)_(—) _(NOMINAL) _(—) _(PUSCH)(j) provided from higher layers for j=0 and1 and a UE specific component P_(O) _(—) _(UE) _(—) _(PUSCH)(j) providedby higher layers for j=0 and 1. α(j) is a specific parameter provided byhigher layers. PL is the downlink pathloss estimate calculated in theUE. Δ_(TF)(i) is a UE specific parameter. f(i) is a UE specific valueobtained from a transmit power control (TPC) command.

The setting of the UE Transmit power P_(PUCCH) for the PUCCHtransmission in subframe i is defined by:

MathFigure 4P _(PUCCH)=min{P _(CMAX) ,P _(O) _(—) _(PUCCH) +PL+h(n _(CQI) ,n_(HARQ))+Δ_(F) _(—) _(PUCCH)(F)+g(i)}  [Math. 4]

where P_(CMAX) and PL are same as the equation 3, and P₀ _(—) _(PUCCH)is a parameter composed of the sum of a cell specific parameter P₀ _(—)_(NOMINAL) _(—) _(PUCCH) provided by higher layers and a UE specificcomponent P₀ _(—) _(UE) _(—) _(PUCCH) provided by higher layers.h(n_(CQI),n_(HARQ)) is a PUCCH format dependent value. Δ_(F) _(—)_(PUCCH)(F) is a parameter provided by higher layers. g(i) is a UEspecific value obtained from a transmit power control (TPC) command.

Hereinafter, multiple antenna transmission in uplink is disclosed.

FIG. 10 is a diagram showing an example in which an ACK/NACK signal istransmitted via a multi-antenna.

The time, frequency, and/or code resources used to transmit an ACK/NACKsignal are referred to as ACK/NACK resources or PUCCH resources. Asdescribed above, the index of an ACK/NACK resource (also referred to asan ACK/NACK resource index or a PUCCH index) necessary to transmit theACK/NACK signal on PUCCHs can be expressed into at least any one of theorthogonal sequence index i, the CS index I_(cs), the resource blockindex m, and indices for finding the three indices. The ACK/NACKresource can include at least any one of an orthogonal sequence, a CS, aresource block, and a combination of them.

Although the ACK/NACK resource index is illustrated to be the aboveresource index n⁽¹⁾ _(PUCCH) in order to clarify the description, theconfiguration or expression of the ACK/NACK resource is not limited.

A modulation symbol s1 of an ACK/NACK signal is transmitted through afirst antenna 601 using a first ACK/NACK resource and transmittedthrough a second antenna 602 using second ACK/NACK resources.

A first orthogonal sequence index i₁, a first CS index I_(cs1), and afirst resource block index m₁ are determined based on a first ACK/NACKresource index, and a first PUCCH is configured based on the determinedindices. A second orthogonal sequence index i₂, a second CS indexI_(cs2), and a second resource block index m₂ are determined based on asecond ACK/NACK resource index, and a second PUCCH is configured basedon the determined indices. The modulation symbol s1 is transmittedthrough the first antenna 601 on the first PUCCH and transmitted throughthe second antenna 602 on the second PUCCH.

Consequently, since the same ACK/NACK signal is transmitted throughdifferent antennas using different resources, transmit diversity gaincan be obtained.

In the conventional 3GPP LTE which only support single antennatransmission, a single ACK/NACK resource is determined on the basis ofresources used to transmit PDCCHs. More specifically, a single resourceindex (i.e., an index of the ACK/NACK resources) is determined on thebasis of the lowest CCE index used to transmit a PDCCH. This scheme

However, two ACK/NACK resources are needed to implement the example ofFIG. 10. This means that a plurality of ACK/NACK resources has to beallocated for multiple antenna transmission.

FIG. 11 is a diagram showing a method of determining a plurality ofresources. In this method, a first ACK/NACK resources are determinedlike the conventional 3GPP LTE, but a second ACK/NACK resources aredetermined on the basis of a CCE index next to the lowest CCE index.

It is assumed that a CCE index 5 used to transmit a PDCCH for a downlinkgrant, from among CCE indices, is the lowest index. If the CCEaggregation level L is 1, a first ACK/NACK resource index P1 isdetermined on the basis of the lowest CCE index 5 as in the existingmethod, and a second ACK/NACK resource index P2 is determined on thebasis of an index 6 subsequent to the lowest CCE index 5. The sameprinciple is applied to CCE aggregation levels L=2, 4, and 8.

If the CCE index next to the lowest CCE index is larger than N_(CCE)−1,the CCE index next to the lowest CCE index may be set to 0 by usingcyclic shift. N_(CCE) is the total number of CCEs.

In other words, the first and second ACK/NACK resource indices P1 and P2may respectively be defined as P1=n_(CCE)+N⁽¹⁾ _(PUCCH) andP2=n_(CCE+1))+N⁽¹⁾ _(PUCCH), respectively, irrespective of their CCEaggregation levels.

Although the second ACK/NACK resource index P2 is illustrated to bedetermined on the basis of an index subsequent to the lowest CCE index,the second ACK/NACK resource index P2 may be determined using(n_(CCE)+b)+N⁽¹⁾ _(PUCCH), more generally. Here, b is a positive ornegative integer.

Now, the proposed uplink transmit power control will be described.

Even if a wireless apparatus supports multiple-antenna transmission, themultipleantenna transmission cannot always be used. Due to any reasonsuch as non-allocation of resources, etc., the wireless apparatus has tobe able to dynamically perform switching between multiple-antennatransmission and single-antenna transmission.

In the example of FIG. 11, if a CCE index 6 is allocated to another UE,a UE obtains only a first ACK/NACK resource and cannot obtain a secondACK/NACK resource. If only one ACK/NACK resource is obtained, the UE cantransmit an ACK/NACK signal through one antenna by using one ACK/NACKresource. That is, multiple-antenna transmission using two antennas isswitched to single-antenna transmission.

When a transmit mode is switched, link capability may deteriorate iftransmit power cannot be effectively controlled.

FIG. 12 is a flowchart showing a transmission power control methodaccording to an embodiment of the present invention.

A UE selects one transmit mode among a plurality of transmit modes (stepS1210). The transmit mode is an uplink transmit mode of the UE usingmultiple antennas or a single antenna.

Transmission using the multiple antennas is referred to as amultiple-antenna transmit mode, and transmission using the singleantenna is referred to as a single-antenna transmit mode.Multiple-antenna transmission can be classified according to the numberof antennas in use. For example, if up to 4 antennas are supported, theUE can dynamically switch the multiple-antenna transmit mode using twoor more antennas and the single-antenna transmit mode using one antenna.The multiple-antenna transmission may use different transmit modes whenthe number of antennas is 2, 3, and 4.

The UE can determine the transmit mode by the instruction of a BS. TheBS can instruct the multiple-antenna transmit mode or the single-antennatransmit mode to the UE by using a higher-layer message or a PDCCH.

The UE can determine the transmit mode on the basis of a resource (i.e.,a PUCCH resource) allocated to uplink transmission. If the number ofPUCCH resources allocated to the UE is greater than 1, themultiple-antenna transmit mode can be determined as the transmit mode,and if the number of PUCCH resources is 1, the singleantenna transmitmode can be determined as the transmit mode.

The UE determines transmit power of an uplink channel on the basis ofthe selected transmit mode (step S1220). The transmit power can bedetermined on the basis of a transmit power offset Δ(M) depending on thetransmit mode. M denotes the transmit mode.

For example, it is assumed that M=1 denotes a single-antenna transmitmode, M=2 denotes a multiple-antenna transmit mode using two antennas(or two resources), M=3 denotes a multiple-antenna transmit mode usingthree antennas (or three resources), and M=4 denotes a multiple-antennatransmit mode using four antennas (or four resources). The UE determinesone transmit power offset among Δ(1), Δ(2), Δ(3), and Δ(4) according tothe selected transmit mode.

The UE determines the transmit power offset Δ(M) according to thetransmit mode, and can add the determined transmit power offset to thetransmit power of the uplink channel.

When the transmit mode is considered, transmit power P_(PUSCH) for PUSCHtransmission of Equation 3 can be modified as follows.

MathFigure 5P _(PUSCH)=min{P _(CMAX),10 log₁₀(M _(PUSCH)(i))+P _(O) _(—)_(PUSCH)(j)+α(j)PL+Δ _(TF)(i)+Δ(M)+f(i)}  [Math. 5]

In addition, transmit power P_(PUCCH) for PUCCH transmission of Equation4 can be modified as follows.

MathFigure 6P _(PUCCH)=min{P _(CMAX) ,P ₀ _(—) _(PUCCH) +PL+h(n _(CQI) ,n_(HARQ))+Δ_(F) _(—) _(PUCCH)(F)+Δ(M)+g(i)}  [Math. 6]

The above equation is for exemplary purposes only, and thus variousmodifications can be made by those ordinary skilled in the art. Forexample, the transmit power offset Δ(M) can be included in a UE-specificparameter (e.g., Δ_(TF)(i), f(i), Δ_(F) _(—) _(PUCCH) (F), and g(i))used to calculate the transmit power.

The UE transmits the uplink channel by using the transmit power (stepS1230). When an ACK/NACK signal is transmitted using two antennas andtwo PUCCH resources, the ACK/NACK signal can be transmitted as shown inFIG. 10.

When the UE switches from the multiple-antenna transmit mode to thesingleantenna transmit mode, if the UE performs single-antennatransmission while maintaining the same transmit power as that used inmultiple-antenna transmission, link capability may deteriorate.

For example, it is assumed that two PUCCH resources are allocated to theUE, and the UE transmits an ACK/NACK signal through two antennas in themultiple-antenna transmit mode. It is also assumed that transmit powerof each transmit antenna is X dBm. In this case, total transmit power isX+3 dBm.

When one PUCCH resource is allocated to the UE for a certain reason, theUE can be switched to the single-antenna mode. In this case, if thetransmit power maintains the previous transmit power X dBm, linkcapability may deteriorate. The previous transmit power X dBm isdesigned by considering a transmit diversity gain. This is because thetransmit diversity gain decreases in the single-antenna transmission.

Therefore, the proposed method allows the UE to control the transmitpower of the uplink channel according to the transmit mode.

The less the number of antennas in use, the greater the transmit poweroffset Δ(M) can be set. For example, Δ(2) can be set to 0, and Δ(1) canbe set to K (where K is a positive integer).

The transmit power offset Δ(M) can be pre-defined.

The BS can send information for obtaining the transmit power offset Δ(M)to the UE. The BS can send a transmit power offset depending on eachtransmit mode, or send a difference between a transmit power offset ofone transmit mode and a transmit power offset of the remaining transmitmodes. The information can be transmitted by using system information,an RRC message, a MAC message, or a PDCCH.

The transmit power offset Δ(M) can vary depending on a PUCCH format.This is because a compensation value of the transmit power may differsince the transmit diversity gain varies depending on the PUCCH format.

FIG. 13 is a block diagram showing a wireless apparatus for implementingan embodiment of the present invention. The wireless apparatus may be apart of a UE and implements the embodiment of FIG. 12.

A wireless apparatus 1300 includes a data processor 1310, a transmitpower controller 1320, a transceiver 1330, and a plurality of antennas1340.

The data processor 1310 implements encoding/decoding andmodulation/demodulation of traffic data and/or control signals (e.g.,CQI and ACK/NACK).

The transmit power controller 1320 controls transmit power of an uplinkchannel. As shown in the embodiment of FIG. 12, the transmit powercontroller 1320 can determine a transmit mode, and can determine thetransmit power of the uplink channel on the basis of the transmit mode.

The transceiver 1330 transmits the traffic data and/or the controlsignals through one or more antennas 1340 on the uplink channel by usingthe transmit power.

The data processor 1310, the transmit power controller 1320, and thetransceiver 1330 can be implemented by one processor, chipset, orlogical circuit.

The antenna is also referred to as an antenna port, and may be aphysical antenna or a logical antenna. One logical antenna may includeone or more physical antennas.

In view of the exemplary systems described herein, methodologies thatmay be implemented in accordance with the disclosed subject matter havebeen described with reference to several flow diagrams. While forpurposed of simplicity, the methodologies are shown and described as aseries of steps or blocks, it is to be understood and appreciated thatthe claimed subject matter is not limited by the order of the steps orblocks, as some steps may occur in different orders or concurrently withother steps from what is depicted and described herein. Moreover, oneskilled in the art would understand that the steps illustrated in theflow diagram are not exclusive and other steps may be included or one ormore of the steps in the example flow diagram may be deleted withoutaffecting the scope and spirit of the present disclosure.

The invention claimed is:
 1. A method for transmitting a control signalin a wireless communication system, the method comprising: determining,by a user equipment (UE), a first physical uplink control channel(PUCCH) resource for a first antenna port and a second PUCCH resourcefor a second antenna port; and transmitting, by the UE, a PUCCH via thefirst antenna port and the second antenna port by using the first PUCCHresource and the second PUCCH resource based on an uplink transmitpower, wherein the uplink transmit power P_(PUCCH)(i) at subframe i isdetermined by:P _(PUCCH)(i)=min{P _(CMAX(i)) , P ₀ _(—) _(PUCCH) PL+h(n _(CQI) , n_(HARQ))+Δ_(F) _(—) _(PUCCH)(F)+Δ(M)+g(i)} where P_(CMAX(i)) is aconfigured UE transmit power in subframe i, P₀ _(—) _(PUCCH) is aparameter composed based on provisions by a higher layer, Δ_(F) ₁₃_(PUCCH)(F) is a parameter provided by the higher layer, h(n_(COI),n_(HARQ)) is a PUCCH format dependent value, PL is a downlink pathlossestimate calculated in the UE, g(i) is a value related to a UE specificvalue, and Δ(M) is an offset value when the PUCCH is transmitted via thefirst antenna port and the second antenna port.
 2. The method of claim1, wherein Δ(M)=0 when the PUCCH is transmitted via one antenna port. 3.The method of claim 1, wherein a list of values of Δ(M) is provided by abase station in accordance with PUCCH formats.
 4. The method of claim 3,wherein the PUCCH formats are defined by: PUCCH Format Modulation SchemeNumber of Bits per subframe 1 N/A N/A 1a BPSK 1 1b QPSK 2 2 QPSK 20 2aQPSK + BPSK 21 2b QPSK + BPSK 22


5. The method of claim 1, wherein the PUCCH carries at least one of ascheduling request, an ACK/NACK for hybrid automatic repeat request(HARQ) and a channel quality indicator (CQI).
 6. The method of claim 1,further comprising: receiving information about a transmission mode froma base station, the transmission mode indicating that the PUCCH istransmitted via one antenna port or two antenna ports.
 7. A userequipment (UE) in a wireless communication system, the UE comprising: afirst antenna port; a second antenna port; a transceiver configured to:determine a first physical uplink control channel (PUCCH) resource for afirst antenna port and a second PUCCH resource for a second antennaport, and transmit a PUCCH via the first antenna port and the secondantenna port by using the first PUCCH resource and the second PUCCHresource based on an uplink transmit power; and a transmit powercontroller configured to determine the uplink transmit powerP_(PUCCH)(i) at subframe i by:P _(PUCCH)(i)=min{P _(CMAX(i)) , P ₀ _(—) _(PUCCH) +PL+h(n _(CQI) , n_(HARQ))+Δ_(F) _(—) _(PUCCH)(F)+Δ(M)+g(i)} where P_(CMAX(i)) is aconfigured UE transmit power in subframe i, P₀ _(—) _(PUCCH) is aparameter composed based on provisions by a higher layer, Δ_(F) _(—)_(PUCCH)(F) is a parameter provided by the higher layer, h(n_(COI),n_(HARQ)) is a PUCCH format dependent value, PL is a downlink pathlossestimate calculated in the UE, g(i) is a value related to a UE specificvalue, and Δ(M) is an offset value when the PUCCH is transmitted via thefirst antenna port and the second antenna port.
 8. The UE of claim 7,wherein Δ(M)=0 when the uplink control channel is transmitted via oneantenna port.
 9. The UE of claim 7, wherein a list of values of Δ(M) isprovided by a base station in accordance with PUCCH formats.
 10. The UEof claim 9, wherein the PUCCH formats are defined by: PUCCH FormatModulation Scheme Number of Bits per subframe 1 N/A N/A 1a BPSK 1 1bQPSK 2 2 QPSK 20 2a QPSK + BPSK 21 2b QPSK + BPSK 22


11. The UE of claim 7, wherein the PUCCH carries at least one of ascheduling request, an ACK/NACK for hybrid automatic repeat request(HARQ) and a channel quality indicator (CQI).
 12. The UE of claim 7,wherein the transceiver is configured to receive information about atransmission mode from a base station, the transmission mode indicatingthat the uplink control channel is transmitted via one antenna port ortwo antenna ports.